One unique aspect of 193i lithography is the use of water situated between the final lens element and the resist. The resist stack (with or without topcoat) on the wafer is dynamically exposed through this water with the step-and-scan process. The photoacid generator (PAG), quencher, and other small molecular components of the resist may leach into this water. These leached components contaminate the water and may degrade resist performance. This contaminated water can additionally contaminate the lens and wafer stage of the scanner. To master these leaching problems, we must understand the dynamics of resist leaching, transportation of leached contaminates in the immersion water, and the impact of these contaminants on the lens during exposure.Additionally, water can penetrate the topcoat and diffuse into the resist film. This penetration and diffusion of water can cause the topcoat or the resist to swell, which will affect their lithographic performance. This chapter specifically addresses the following issues: (1) leaching test methods, (2) leaching dynamics, (3) leaching with 193-nm exposure, (4) pre-rinse to partially remove leached contaminants, (5) lens contamination caused by resist leaching, and (6) water uptake in resist film.
Successful developer-soluble topcoats have to fulfill numerous requirements; specifically they have to serve as a barrier layer and be compatible with the resist. Some of the requirements and compatibility issues have been understood; others are still under-investigation by the joint efforts of lithographers and resist chemists. This paper addresses these requirements from the perspective of overall lithographic performance for developer-soluble topcoats used in 193nm water immersion lithography. We demonstrate that with the optimized combination of resist and developer-soluble topcoat 90nm 1:1 dense lines can be printed using a prototype tool, ASML AT 1150i, and a binary image mask (BIM) with a maximum depth-of-focus (DOF) of ~1.2µm. An approximate 2X DOF improvement over dry lithography that was theoretically expected has been truly demonstrated. Topcoat related defectivity as well as defect reduction efforts are also discussed.
193nm immersion resist without topcoat is production preferred solution. The challenge of 193nm immersion resist is both low leaching level and high performance. This paper summarizes the screening results of selected 193nm immersion resists which are designed for use without top coatings. Our evaluation is divided into several phases. Leaching levels of resist samples were first tested. The leaching data were analyzed and compared to our specifications. Both binary image mask and alternating phase-shift mask exposures were done to evaluate the process window, lineedge roughness, and resist pattern profile. Resist films were rinsed by DI water prior to or after exposure, and contrast curves were measured to investigate the resist sensitivity change. The results are compared with resist systems which use developer-soluble topcoats.
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